Field of the Invention
The present invention relates to an electrolyte material formulation, an electrolyte material composition formed from the electrolyte material formulation, and a solid capacitor using the electrolytic material composition.
Description of the Related Art
Capacitors are a type of electronic elements that are widely used in various electronic products. With advancement in technology development, electronic products are being developed in the direction of miniaturization and light weight, and the capacitors used in electronic products are required to be miniaturized and have a high capacitance and low impedance when being used at a high frequency.
Capacitors may be classified into conventional liquid capacitors and newly developed solid capacitors. In the electrolyte of early-stage aluminum liquid capacitor, a liquid electrolyte is used as a charge transfer substance. The main components of the liquid electrolyte include a high-boiling point alcohol, an ionic liquid, boric acid, phosphoric acid, an organic carboxylic acid, an ammonium, a high-polarity organic solvent, and a small amount of water. The components not only serve as charge transfer substances, but also have the function of patching a dielectric layer of aluminum oxide on an aluminum foil. If the internal aluminum metal is exposed due to defects on the dielectric layer of aluminum oxide, during the charge and discharge process of the capacitor, the electrolyte may react with the exposed aluminum metal and aluminum oxide is generated, thus achieving the patching function. However, although the conventional aluminum liquid capacitor can meet the requirement of high capacitance at a low cost, as the electrolyte used is a liquid, it has the disadvantages of low conductivity and poor high temperature resistance; moreover, in the process of aluminum oxide generation, hydrogen is also generated, and if excessive hydrogen is accumulated in the capacitor, capacitor rupture can easily occur, which will damage the electronic product. Although a hydrogen absorbing agent may be added to the liquid electrolyte to reduce the risk of capacity rupture, the problem is not eliminated.
Accordingly, a new generation of solid capacitor is developed, in which the liquid electrolyte is directly replaced by a solid electrolyte. The solid electrolyte is formed by a conductive polymer. Anions of an oxidant are blended in the structure of the polymer as a dopant and holes are formed, so that the polymer has conductivity. Compared with the liquid electrolyte or a solid organic semiconductor complex salt such as tetracyanoquinodimethane (TCNQ) composite salt and inorganic semiconductor MnO2 used in conventional electrolyte capacitor, the conductive polymer has a high conductivity and a suitable high high-temperature insulation property, so the conductive polymer has propelled the development of the trend of using solid electrolyte in current electrolytic capacitors.
In addition to having long service life that is 6 times longer than that of a common capacitor, the solid capacitor has improved stability and its capacitance is not easily influenced by an ambient temperature and humidity in use. Additionally, the solid capacitor has the advantage of a low ESR, a low capacitance variation rate, an excellent frequency response (high frequency resistance), a high temperature resistance, and a high current resistance, and the problem of leakage and plasma explosion is eliminated. Although conventional liquid capacitor has high capacitance, its application is limited due to a high ESR.
Jesse S. Shaffer et al disclose a method of using a conductive polymer in an electrolyte of an electrolytic capacitor for the first time in U.S. Pat. No. 4,609,971. The method includes immersing an anode aluminum foil of a capacitor in a mixture solution formed by a conductive polymer polyaniline powder and a dopant LiClO4, and then removing a solvent on the aluminum foil. Due to its excessively high molecular weight, polyaniline cannot permeate into micropores of the anode foil, so the impregnation rate of the capacitor obtained through this method is poor, and the impedance is high. Then, in order to enable the polymer to easily permeate into the micropores of the anode foil, Gerhard Hellwig et al disclose a chemical oxidation polymerization method of using a conductive polymer as an electrolyte of a capacitor in U.S. Pat. No. 4,803,596. The method includes respectively immersing a capacitor anode foil in a solution of a conductive polymer monomer and an oxidant, and polymerizing the conductive polymer monomer at a suitable condition, in which the conductive polymer electrolyte is accumulated to a sufficient thickness through multiple immersions. Thereafter, Friedrich Jonas et al of the Bayer Corporation in Germany disclose a method of manufacturing an aluminum solid capacitor with poly-3,4-ethylenedioxythiophene (PEDOT) as an electrolyte by using a monomer 3,4-ethylenedioxythiophene (EDOT) in combination with an oxidant iron (III) p-toluenesulfonate for the first time in U.S. Pat. No. 4,910,645. Moreover, it has been found that 3,4-ethylenedithiathiophene (EDTT) which is structurally related to EDOT can be converted to electroactive polymer (see Lambertus Groenendaal et. Al, Adv. Mater. 2000, 12, No. 7).
The conductive polymer PEDOT has the advantages of a high heat resistance, a high conductivity, a high charge transfer velocity, being non-toxic, a long service life, and no occurrence of capacitor rupture when being applied in a capacitor. Presently, almost all solid capacitor manufacturers use the two materials to manufacture aluminum or tantalum solid capacitor. However, PEDOT on the aluminum foil surface or pores that is polymerized by immersing the capacitor element in a mixture solution containing the monomer EDOT and iron (III) p-toluenesulfonate mostly has a powder structure with a lower polymerization degree, and the physical properties of the powder structure are poor, so the powder structure cannot be easily adhered on the aluminum foil surface or pores as it is more likely to fall off from the surface or pores, and a complete PEDOT polymer structure cannot be easily formed on the aluminum foil surface or pores. Therefore, the stability of the solid capacitor at a voltage of 16 V or higher is poor, resulting in that the solid capacitor cannot be used in the process of a voltage of 16 V or higher, or the yield of the process is low. Moreover, since the powder structure formed by the conductive polymer PEDOT cannot be easily adhered on the aluminum foil pores, when the problem of falling off occurs, the withstandable working voltage is limited.
In Japanese Patent No. 2010-129651, it is disclosed that a capacitor element is directly immersed in a polymer solution containing a polymer PEDOT, and a complete PEDOT polymer structure is formed on an aluminum foil surface or pores, so that a solid capacitor is applicable in a working environment of a voltage of 50 V. However, when compared with conventional process, the cost of the polymer PEDOT material is higher than that of the monomer EDOT; the polymer PEDOT material is difficult to store; and the process needs more time and is more difficult to control.
Accordingly, the industry calls for the development of a solid capacitor that can withstand a higher voltage, such as 50 V or more, has good stability and is priced at a relatively low cost, so as to replace the liquid capacitor in 3C products that require high temperature resistance and high frequency resistance.